[Bug 101619] [SKL] DPCD backlight causes black screen on ThinkPad X1 Carbon 4th Gen

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101619

--- Comment #11 from David Weinehall <david.weinehall at intel.com> ---
It seems that the issue is with DBC rather than DPCD backlight as I first
thought; reverting the DBC patch (or disabling dbc) seems to be enough to get
things working.

Setting min=100, max=100 didn't solve anything, neither did min=40, max=60
(just in case the display has some weird hangup about 100%).

The patch that introduces the issue is:

ae25eceab616d16a07bcaa434b84463d58a3bdc3

On a somewhat tangential note, having DBC enabled by default feels very
dubious, in my opinion, especially since it's not a user adjustable option. If
there's no way to toggle DBC on/off from userspace I much rather adjust the
brightness using Fn + F5/F6 than have the system decide what's best for me.

This of course only applies if it's a strict choice between DBC & manual
control; if the DBC only adjust the brightness already set by the user, then
it's a different story, obviously.

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